Hi.
For now I use this straps https://www.decathlon.pl/p/paski-turystyczne-wielofunkcyjne-10-mm-x2/_/R-p-338645?mc=8736108 to mount my tripod to bicecles frame upper pipe (horisontal).
But hooking and unhooking takes long time.
Maybe You know any pouch for tripod which is ready to mount to bicycle frame ?
Darek
I donāt know of exactly what you asked for, but couldnāt you attach the tripod (with or without the bag it may have come in) to the top tube of your bike with a couple of bungee cords?
(BTW, something as thick as a tripod attached to your top tube might make for uncomfortable cycling)
The crossbar wouldnāt give enough room for the tripod between my legs.
I used to strap a tripod horizontally to the rear rack. (That also works for crutches.)
I think a better solution would be a simple custom bag made of leatherette, or an adapted shop-bought pannier, hanging vertically on one side of the rear rack, securely strapped to the bike. The bag would have a top flap closed with velcro to keep the rain out, and the tripod in while riding over potholes. Putting the tripod (or crutches) in or out of the bag would take only a few seconds.
Tripod should be a piece of cakeā¦ 
Exactly.
This is what I did.
My āupper pipeā this is Your ātop tubeā. My english is more mine than english 
Straps from Decathlon this is bungee cord.
I would fix a drain pipe in that space, a bit of cushioning in it and a bungee cord for fixing.
I seem to remember (or perhaps I imagined) someone mounted a tripod head on the rear rack. The bike also had a stand. Hence the bike itself became a tripod, and there was no need to carry separate legs.
I was trying this solution, but (my) bicycle is not stable for this purpose
German Berlebach makes a few:
I would solder/screw an arca-swiss plate upside down somewhere, and then the tripod will hang by itselfā¦
Camera mounted on the bike with a stand was the 19th century solutionā¦